Robust variable star detection techniques suitable for automated searches: new results for NGC 1866

We describe sensitive techniques for identifying variable stars in multiepoch photometry lists made in two or more bandpasses or pairwise in a single bandpass. Our search strategy employs the correlation in brightness change between paired frames, which allows the extraction of information on variability in the presence of random photometric noise. A statistic for assessing the type of variable or degree of contamination by an unresolved source (depending on circumstance) is also described, as well as a bootstrap scheme for predicting confidence intervals for detection of real variability. These detection schemes are manifestly more robust than existing search techniques. To illustrate the power of this technique, we give a two-epoch example for photometry in the field of NGC 3201, a globular cluster rich in RR Lyr variables